Lubrication of windmilling journal bearings

ABSTRACT

A support shaft provides lubrication to a journal bearing during windmilling operation of a gear set. A primary oil pump provides oil from an oil supply during driven operation of the fan, and a secondary oil pump provides oil from an internal sump during windmilling operation of the fan. During driven operation of the fan, oil is pumped with the primary oil pump through a primary oil flow path to an outer surface of the support shaft. During windmilling fan operation, oil is pumped from an internal sump with a secondary oil pump through the secondary oil flow path. The secondary oil flow path has a smaller flow capacity, and the secondary oil pump is a smaller capacity pump.

BACKGROUND OF THE INVENTION

This invention relates to an arrangement for supplying oil to journalbearings for use in fan drive systems for turbofan engines.

Turbine engines use epicyclic gear systems to drive fans or propellersduring engine operation. Journal bearings are utilized in the gearsystems to transfer torque between planet gears and correspondingsupport shafts. Oil is supplied from an oil system to lubricate each ofthe journal bearings. An oil pump maintains pressure within the oilsystem to ensure each of the journal bearings receives an adequatesupply of oil.

During operation, the gas turbine can be shut down for various reasons.When the gas turbine is not operating, the oil pump may also shut down.However, due to the force of the wind, the fan will continue to rotate,or windmill, even while the engine is not driving the fan. Without someoil supply, the journal bearings may seize and stop engine rotation.

The required oil supply for a windmilling fan is significantly reducedcompared to driven fan operation. Thus, the size of the oil lines usedfor driven fan operation is larger than the size of the oil lines neededfor a windmilling fan. A pressure drop across all bearings would occurif using the same oil lines at significantly reduced flow, resulting inonly some of the bearings receiving oil. Also, in the event of systemoil loss, a separate system to supply oil to the bearings forwindmilling is required.

Accordingly, providing an improved arrangement to lubricate journalbearings during windmilling fan operation is desired.

SUMMARY OF THE INVENTION

An example journal bearing according to this invention provideslubrication to a planet gear during windmilling operation of a gearsystem.

During engine operation, a fan for a turbine engine is driven by a fandrive gear system including an epicyclic gear set. An oil supply systemsupplies oil to lubricate the epicyclic gear set. When the engine in notoperating, wind passing through the fan can cause the fan to rotate, orwindmill, even though the fan is not being driven by the fan drive gearsystem.

Each planet gear within the epicyclic gear set has a journal bearinglocated between a planet gear and a support shaft. The journal bearingstransfer torque between the planet gears and the support shafts. Duringdriven operation of the fan, oil is pumped by the primary oil pumpthrough a primary oil flow path to an outer surface of the supportshaft.

During windmilling fan operation, the planet gears continue to rotate inthe same rotational direction at a slower rotational speed. Because ofthe slower speed, less oil is required to lubricate the journalbearings. Oil is pumped from an internal compartment sump with asecondary oil pump through a secondary oil flow path. The secondary oilflow path has a smaller flow capacity, and the secondary oil pump is asmaller capacity pump.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a portion of an example turbine engine ofthe present invention;

FIG. 2 schematically illustrates a fan drive system for a fan of theexample turbine engine;

FIG. 3 illustrates an example epicyclic gear set;

FIG. 4 a illustrates a front view of an example journal bearingillustrating oil flow during driven operation of the fan;

FIG. 4 b illustrates a side view of the example journal bearingillustrating oil flow during driven operation of the fan;

FIG. 5 a illustrates a front view of the example journal bearingillustrating oil flow during windmilling operation of the fan; and

FIG. 5 b illustrates a side view of the example journal bearingillustrating oil flow during windmilling operation of the fan.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic view of a portion of a turbine engine 10. Theturbine engine 10 includes a fixed housing 12 that is constructed fromnumerous pieces secured to one another. A compressor section 14 hascompressor hubs 16 with blades. A turbine shaft 25 drives the hubs 16about an axis A. A fan 18 is supported on a fan shaft 20 that is drivenby a turbine flexible coupling 30 through a gear set 28.

FIG. 2 schematically illustrates a fan drive system 26 for the fan 18.The gear set 28 is preferably an epicyclic gear set including theturbine flexible coupling 30, which drives the fan 18. An oil supplysystem 32 supplies oil to the epicyclic gear set 28. The oil supplysystem 32 includes a primary oil pump 34 which provides oil from an oilsupply 36 during driven operation of the fan 18. A secondary oil pump 38provides oil from an internal sump 35 during windmilling operation ofthe fan 18.

Referring to FIG. 3, an example epicyclic gear set 28 is illustrated. Asun gear 40 is mounted to the turbine flexible coupling 30. A pluralityof planet gears 42 engage the sun gear 40. In the embodiment shown,there are five planet gears 42. A support shaft 44 supports each planetgear 42. A journal bearing 46 is defined between each of the planetgears 42 and the support shafts 44. The planet gears 42 rotate relativeto the support shaft 44. The journal bearings 46 transfer torque betweenthe planet gears 42 and the support shafts 44. A coating is applied toan inner surface 50 of each planet gear 42. The coating contacts thesupport shaft 44 only during startup and shutdown of the engine 10.

FIGS. 4 a and 4 b illustrate the oil flow through the support shaft 44during driven operation of the fan 18. The planet gear 42 with thecoating rotates around the support shaft 44. The inner surface 50 of theplanet gear 42 is adjacent to an outer surface 54 of the support shaft44. A space 56 between the inner surface 50 and the outer surface 54allows oil to flow between the support shaft 44 and the planet gear 42.The support shaft 44 remains stationary and the planet gear 42 rotates,as indicated by arrow R.

Oil is pumped from the oil supply 36 with a primary oil pump 34 (shownin FIG. 2). The oil from the primary oil pump 34 enters the supportshaft 44 from a first side 58 of the support shaft 44. The oil flowsthrough a primary oil flow path 60 to the outer surface 54 of thesupport shaft 44. The oil flows into the space 56 between the outersurface 54 of the support shaft 44 and the inner surface 50 of theplanet gear 42.

FIGS. 5 a and 5 b illustrate the oil flow through the support shaft 44during windmilling operation of fan 18. The planet gear 42 continues torotate in the same rotational direction as it was rotating during drivenfan 18 operation. However, the planet gear 42 is moving at a slowerrotational speed. Because of the slower speed and load, there is lessoil required. Additionally, the primary oil pump 34 may not beoperating, which can lower the pressure within the primary oil flow path60.

The oil is pumped from the internal sump 35 with the secondary oil pump38 (shown in FIG. 2). The secondary oil pump 38 may be activated tobegin pumping when a predetermined minimum pressure is measured withinthe oil supply system 32. Continuous operation or other arrangements foractivating the secondary oil pump 38 may also be utilized. The secondaryoil pump 38 pumps oil to the support shaft 44 from a second side 62 ofthe support shaft 44, and the oil enters a secondary oil flow path 64.Less oil is required to lubricate the space 56 between the outer surface54 of the support shaft 44 and the inner surface 50 of the planet gear42 because of the slow rotational speed of the planet gear 42 and thelower load. The secondary oil flow path 64 has a smaller flow capacitythen the primary oil flow path 60. That is, the secondary oil flow path64 has a smaller diameter passage. Additionally, the secondary oil pump38 may be a smaller capacity pump than the primary oil pump 34 becauseless pressure and volume is required to support the planet gear 42.

The support shaft 44 of the present invention is described for use withturbine engines. However, the support shaft 44 may be used in epicyclicgear sets 28 providing drive for other applications.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. An epicyclic gear set comprising: a sun gear; a plurality of planetgears arranged around and driven by the sun gear; and a plurality ofsupport shafts each associated with one of the plurality of planetgears, wherein each of the plurality of support shafts has a primary oilflow path for supplying oil during driven gear operation and a secondaryoil flow path for supplying oil when the sun gear is not driving theplurality of planet gears, wherein, during driven gear operation, theoil flows through the primary oil flow path and does not flow though thesecondary oil flow path, and wherein, when the sun gear is not drivingthe plurality of planet gears, the oil flows through the secondary oilflow path and does not flow through the primary oil flow path.
 2. Theepicyclic gear set of claim 1, wherein the primary oil flow path enterseach of the plurality of support shafts from a first side and thesecondary oil flow path enters each of the plurality of support shaftsfrom a second side opposite to the first side.
 3. The epicyclic gear setof claim 1, wherein the primary oil flow path has a larger flow capacitythan the secondary oil flow path.
 4. The epicyclic gear set of claim 1,wherein the oil within the primary oil flow path is supplied from afirst oil source and the oil within the secondary oil flow path issupplied from a second oil source, wherein the first oil source isdifferent from the second oil source.
 5. The epicyclic gear set of claim1, wherein a primary oil pump pumps the oil to the primary oil flow pathand a secondary oil pump pumps the oil to the secondary oil flow path.6. The epicyclic gear set of claim 1, wherein each of the plurality ofplanet gears are supported by one of the plurality of support shafts todefine a journal bearing between each of the plurality of support shaftsand the plurality of planet gears.
 7. The epicyclic gear set of claim 6,wherein the primary oil flow path and the secondary oil flow path supplythe oil between each of the plurality of support shafts and theplurality of planet gears.
 8. A turbine engine comprising: a turbofan;an epicyclic gear system for driving the fan, the epicyclic gear systemincluding a sun gear and a plurality of planet gears arranged around anddriven by the sun gear; a plurality of support shafts each associatedwith one of the plurality of planet gears, wherein each of the pluralityof support shafts includes a primary oil flow path for supplying oilduring driven gear operation and a secondary oil flow path for supplyingthe oil when the sun gear is not driving the plurality of planet gears;and an oil supply system to supply the oil to the primary oil flow pathand the secondary oil flow path, wherein, during driven gear operation,the oil flows through the primary oil flow path and does not flow thoughthe secondary oil flow path, and wherein, when the sun gear is notdriving the plurality of planet gears, the oil flows through thesecondary oil flow path and does not flow through the primary oil flowpath.
 9. The turbine engine of claim 8, wherein the primary oil flowpath enters each of the plurality of support shafts from a first sideand the secondary oil flow path enters each of the plurality of supportshafts from a second side opposite to the first side.
 10. The turbineengine of claim 8, wherein the primary oil flow path has a larger flowcapacity then the secondary oil flow path.
 11. The turbine engine ofclaim 8, wherein the oil supply system comprises a primary oil source tosupply the oil to the primary oil flow path and an internal sump oilsupply to provide the oil to the secondary oil flow path, wherein theprimary oil source is different from the internal sump oil supply. 12.The turbine engine of claim 8, wherein a primary oil pump pumps the oilto the primary oil flow path and a secondary oil pump pumps the oil tothe secondary oil flow path.
 13. The turbine engine of claim 8, whereineach of the plurality of planet gears are supported by one of theplurality of supports shafts, and a journal bearing is defined betweeneach of the plurality of support shafts and the plurality of planetgears.
 14. The turbine engine of claim 13, wherein the primary oil flowpath and the secondary oil flow path supply the oil between each of theplurality of support shafts and the plurality of planet gears.
 15. Theepicyclic gear set of claim 1, wherein the primary oil flow path istransverse to the secondary oil flow path.
 16. The epicyclic gear set ofclaim 1, wherein the oil within the primary oil flow path is suppliedfrom a first oil source, the oil within the secondary oil flow path issupplied from a second oil source, a primary oil pump pumps the oil fromthe first oil source to the primary oil flow path, a secondary oil pumppumps the oil from the second oil source to the secondary oil flow path,the first oil source is different from the second oil source, and theprimary oil flow path has a larger flow capacity than the secondary oilflow path.
 17. The epicyclic gear set of claim 1, wherein the oil ispumped through the secondary oil flow path when a predetermined minimumpressure is measured within an oil supply system.
 18. The epicyclic gearset of claim 1, wherein the plurality of planet gears are windmillingwhen the sun gear is not driving the plurality of planet gears.
 19. Theturbine engine of claim 8, wherein the primary oil flow path istransverse to the secondary oil flow path.
 20. The turbine engine ofclaim 8, wherein the oil within the primary oil flow path is suppliedfrom a first oil source, the oil within the secondary oil flow path issupplied from a second oil source, a primary oil pump pumps the oil fromthe first oil source to the primary oil flow path, a secondary oil pumppumps the oil from the second oil source to the secondary oil flow path,the first oil source is different from the second oil source, and theprimary oil flow path has a larger flow capacity than the secondary oilflow path.
 21. The turbine engine of claim 8, wherein the oil is pumpedthrough the secondary oil flow path when a predetermined minimumpressure is measured within the oil supply system.
 22. The turbineengine of claim 8, wherein the plurality of planet gears are windmillingwhen the sun gear is not driving the plurality of planet gears.